Space efficient magnetic antenna system

ABSTRACT

A space efficient magnetic antenna is disclosed for use in tracking, positioning and other applications. In a preferred embodiment, a space efficient magnetic antenna system comprises a first magnetic antenna with a first null axis aligned within a predetermined plane and a second magnetic antenna having a second null axis aligned substantially orthogonal to a first null axis. A second magnetic antenna system lies in a minimal coupling orientation with respect to a first magnetic antenna system. Additionally, a first magnetic antenna may further comprise a plurality of interconnected magnetic antenna elements. A space efficient magnetic antenna system may include an RF module. An RF module may alternately utilize a first magnetic antenna and a second magnetic antenna, or an RF module may drive a second magnetic antenna in phase quadrature with respect to a first magnetic antenna. In still further embodiments, a space efficient magnetic antenna system may further include a third mutually orthogonal magnetic antenna.

RELATED APPLICATIONS

The present application is a continuation-in-part of U.S. patentapplication Ser. No. 11/272,533 titled: “Near field location system andmethod,” filed Nov. 10, 2005 by Schantz et al., which claims the benefitunder 35 USC 119(e) of provisional application Ser. No. 60/637,779,titled: “Near field amplitude positioning system and method,” filed Dec.21, 2004 by Schantz et al., which is incorporated herein by reference inits entirety.

This invention was made with Government support under Grant OII-0539073awarded by the National Science Foundation. The government has certainrights in the invention.

Near field electromagnetic ranging was first fully described inapplicant's “System and method for near-field electromagnetic ranging”(Ser. No. 10/355,612, filed Jan. 31, 2003, now U.S. Pat. No. 6,963,301,issued Nov. 8, 2005), which is incorporated herein by reference in itsentirety.

Further details on electromagnetic ranging and positioning are disclosedin U.S. patent application Ser. No. 10/958,165, published as Pub. No. US2005/0046608 A1 titled “Near field electromagnetic positioning systemand method,” filed Oct. 4, 2004 by Schantz et al. and U.S. patentapplication Ser. No. 11/215,699, titled “Low Frequency Asset TagTracking System and Method,” filed Aug. 30, 2005 by Schantz et al. Allof the above listed US Patent and Patent Applications are herebyincorporated herein by reference in their entirety.

BACKGROUND

1. Field of the Invention

The present invention relates generally to antenna systems, particularlyfor use in measurement of position or location by means ofelectromagnetic signaling.

2. Background of the Invention

Magnetic antennas, particularly loopstick antennas, are often used forreception of low frequency signals. FIG. 1 is a circuit diagram showinga prior art loopstick antenna 104. Prior art loopstick antenna 104comprises primary coil 131, ferrite rod 135, secondary coil 133 andtuning means 132. In alternate embodiments, ferrite rod 135 may be iron,some other ferromagnetic material, or even a non-ferromagnetic materialto support primary coil 131. Ferrite rod 135 may also be a bar,cylinder, prism, or other geometric form suitable for supporting primarycoil 131. In alternate embodiments ferrite rod may be dispensed withaltogether if primary coil 131 is sufficiently stiff to maintain asuitable mechanical shape. Secondary coil 133 provides coupling intoprimary coil 131 and means by which prior art loopstick antenna 104 mayfurther couple to an RF device.

FIG. 2 is a schematic diagram illustrating a prior art loopstick antenna104. Primary coil 131 generally comprises turns with normals co-locatedwith loopstick axis 205. Loopstick axis 205 is not only an axis offerrite rod 135, but also a null axis for prior art loopstick antenna104. Pattern of prior art loopstick antenna 104 lies generally alongpattern axis 207. Pattern axis 207 is substantially orthogonal toloopstick axis 205.

A variety of prior art seeks to determine position using signalamplitude, or equivalently signal strength. These efforts are confoundedby the impact of typical multi-path heavy environments which act toconstructively and destructively combine signals in such a fashion as torender typical signal strength ranging schemes wildly inaccurate. Theseimpacts differ for different building types. Different building typespose different propagation environments for electromagnetic signals andeffect a signal strength ranging system in different ways.

Furthermore, existing amplitude or signal strength positioning schemestend to use sub-optimal antenna arrangements that seriously impact theirperformance. Existing antenna arrangements are large and bulky or smalland inefficient. Other existing antenna arrangements are prone toundesirable coupling to a mobile asset or person being tracked.

In view of the foregoing, there is a great need for location systemsthat can operate accurately in many different multi-path heavyenvironments. There is a further need for compact antenna systems toenable portable and mobile operation of the location systems.

BRIEF SUMMARY OF THE INVENTION

These objects and further objects are met by a space efficient antennasystem comprising a first magnetic antenna having a first null axis. Afirst magnetic antenna further comprises a plurality of interconnectedmagnetic elements each with a null axis substantially parallel to afirst null axis.

In further embodiments, a space efficient antenna system may furthercomprise a second magnetic antenna having a second null axis alignedsubstantially orthogonal to a first null axis. A second magnetic antennamay lie in a minimal coupling orientation with respect to a firstmagnetic antenna.

In still other embodiments, a first magnetic antenna comprises a coilwound around a loopstick axis. Turns of the coil lie in planes whosenormals lie at a substantial diagonal angle with respect to a loopstickaxis.

A space efficient magnetic antenna system may further comprise an RFmodule with characteristic physical dimensions. A first null axis maylie at a substantial diagonal angle with respect to a dimension of an RFmodule. A space efficient magnetic antenna system may also be embeddedin clothing. An RF module may alternately utilize a first magneticantenna and a second magnetic antenna, or an RF module may drive asecond magnetic antenna in phase quadrature with respect to a firstmagnetic antenna.

In alternate embodiments, a space efficient magnetic antenna systemcomprises a first magnetic antenna with a first null axis aligned withina predetermined plane and a second magnetic antenna having a second nullaxis aligned substantially orthogonal to a first null axis. A secondmagnetic antenna system lies in a minimal coupling orientation withrespect to a first magnetic antenna system. Additionally, a firstmagnetic antenna may further comprise a plurality of interconnectedmagnetic antenna elements.

Here again, a space efficient magnetic antenna system may furtherinclude an RF module. An RF module may alternately utilize a firstmagnetic antenna and a second magnetic antenna, or an RF module maydrive a second magnetic antenna in phase quadrature with respect to afirst magnetic antenna. In still further embodiments, a first null axismay lie at a substantial diagonal angle with respect to a dimension ofan RF module. A space efficient magnetic antenna system may furtherinclude a third magnetic antenna with a third null axis mutuallyorthogonal to both a first null axis and a second null axis.

A space efficient magnetic antenna system may include a bar with aprincipal axis aligned along an axis of symmetry and along a directionof greatest extent of the bar. In alternate embodiments, a magneticantenna within a system efficient magnetic antenna system may have anull axis not substantially co-parallel with a principal axis.

In still further embodiments, a space efficient magnetic antenna systemmay include a first magnetic antenna and a second magnetic antennasharing a common core. A common core may be characterized by a principalaxis and a secondary axis with a substantial difference in extent alonga secondary axis relative to a principal axis. A space efficientmagnetic antenna system may be further combined with an RF module whichdrives a second magnetic antenna in phase quadrature relative to a firstmagnetic antenna.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a circuit diagram showing a prior art loopstick antennaconfiguration.

FIG. 2 is a schematic diagram illustrating a prior art loopstick antennaarrangement.

FIG. 3A is plot of path gain versus range in free space for electric andmagnetic signals from a small electric transmit antenna as electric andmagnetic signals transition from the near field to the far field.

FIG. 3B is a graphic representation of electric and magnetic field phaserelationships as a function of range for an ideal electrically smallloop in free space.

FIG. 4 is a schematic diagram describing orientation and antennapatterns of a radio frequency (RF) tracking device.

FIG. 5 is a schematic diagram describing a first embodiment of an RFtracking device.

FIG. 6 is a schematic diagram showing second embodiment of an RFtracking device

FIG. 7A is a schematic diagram describing a preferred embodiment RFtracking device

FIG. 7B is a circuit diagram describing a first potential circuitimplementation of magnetic antennas for a preferred embodiment RFtracking device.

FIG. 7C is a circuit diagram describing a second potential circuitimplementation of magnetic antennas for a preferred embodiment RFtracking device.

FIG. 8 is a schematic diagram presenting a slanted loopstick antenna.

FIG. 9 is a schematic diagram describing a slanted loopstick RF trackingdevice

FIG. 10A is a schematic diagram depicting a first configuration of abody mounted electric field antenna.

FIG. 10B is a schematic diagram depicting a second configuration of abody mounted electric field antenna.

FIG. 10C is a schematic diagram showing a potential configuration of abody mounted magnetic field antenna system.

FIG. 11 is a schematic diagram describing a potential configuration of acanine magnetic field antenna system.

FIG. 12 illustrates one embodiment of a positioning system including aforklift.

FIG. 13 is a schematic diagram depicting a potential configuration of apallet magnetic field antenna system.

FIG. 14 is a process flow diagram of a positioning system employing adual magnetic transmit antenna configuration in accordance with thepresent invention.

FIG. 15 is a process flow diagram of a dual receive antenna positioningprocess in accordance with the present invention.

FIG. 16 is a block diagram showing a preferred embodiment magneticantenna transmission system for use in a positioning system

FIG. 17A is a timing diagram showing a typical clock (C) signal in apreferred embodiment magnetic antenna transmission system.

FIG. 17B is a timing diagram showing a typical in-phase (I) signal in apreferred embodiment magnetic antenna transmission system.

FIG. 17C is a timing diagram showing a typical quadrature (Q) signal ina preferred embodiment magnetic antenna transmission system.

FIG. 18 is a block diagram showing a first alternate embodiment magneticantenna transmission system for use in a positioning system.

FIG. 19 is a block diagram showing a second alternate embodimentmagnetic antenna transmission system for use in a positioning system.

FIG. 20 is a block diagram showing a preferred embodiment magneticantenna reception system for use in a positioning system.

FIG. 21 is a block diagram showing a mobile locator tag for use in apositioning system.

FIG. 22 is a block diagram presenting a fixed beacon transmitter for usein a positioning system.

FIG. 23 is a block diagram describing a fixed locator receiver for usein a positioning system.

FIG. 24 is a block diagram laying out a mobile transmitter tag for usein a positioning system.

FIG. 25 illustrates an exemplary indoor deployment of a positioningsystem including fixed locator receivers and mobile transmitter tags.

FIG. 26 illustrates an exemplary indoor deployment of a positioningsystem including fixed beacon transmitters and mobile locator receivertags.

FIG. 27 illustrates an exemplary positioning system including fixedbeacon transmitters and mobile locator receiver tags at an incidentscene.

FIG. 28 is a process flow diagram of a positioning system includingfixed beacon transmitters and mobile locator tags using near fieldsignal strength.

FIG. 29 shows the geometry around two small orthogonal loops.

FIG. 30 shows the geometry around two small orthogonal loops in a firstminimal coupling arrangement.

FIG. 31 shows the geometry around two small orthogonal loops in a secondminimal coupling arrangement.

FIG. 32 shows a space efficient magnetic antenna system with two smallorthogonal loop antennas in a first minimal coupling arrangement for acompact tracking device.

FIG. 33 shows a space efficient magnetic antenna system with two smallorthogonal loop antennas in a second minimal coupling arrangement for acompact tracking device.

FIG. 34 presents a potential circuit diagram for a magnetic loopstickantenna.

FIG. 35 shows a space efficient magnetic antenna system with a smallorthogonal loop antenna characterized by a null axis orthogonal to aprincipal axis.

FIG. 36 shows a space efficient magnetic antenna system with threemutually orthogonal antennas on a common ferrite.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Overview of theInvention

The present invention is directed to a near field location system andmethod. The present invention will now be described more fully in detailwith reference to the accompanying drawings, in which the preferredembodiments of the invention are shown. This invention should not,however, be construed as limited to the embodiments set forth herein;rather, they are provided so that this disclosure will be thorough andcomplete and will fully convey the scope of the invention to thoseskilled in the art. Like numbers refer to like elements throughout.

Near Field Propagation

A near field location system may rely on certain properties of nearfield electromagnetic signals. FIG. 3A is plot of path gain versus rangein free space for electric and magnetic signals from a small electrictransmit antenna as electric and magnetic signals transition from thenear field to the far field. At a range approximately equal to about onesixth of a wavelength (λ/2π), electromagnetic signals from electricallysmall antennas in free space transition between near field to far fieldbehavior. In the near field zone, within λ/2π, “like” signals decreasein amplitude 60 dB for every decade (factor of ten) increase in range,as shown in trace 301. “Like” signals are signals received by an antennaof the same type of design e.g. electric fields received by electricfield antenna such as a dipole or whip antenna or magnetic fieldsreceived by a magnetic antenna such as a loop or loopstick antenna. Alsoin the near field zone, “unlike” signals (electric signals from magneticantennas or magnetic signals from electric antennas) decrease inamplitude 40 dB for every decade increase in range, as shown in trace302. In the transition region around λ/2π, both like and unlike signalstransition to far field behavior in which signals decrease in amplitude20 dB for every decade increase in range, as shown in trace 303. Thistransition is essentially complete once signals propagate one wavelength(1λ). Thus it is advantageous for a signal strength positioning systemto operate at ranges on the order of 1λ or less. Conversely it isadvantageous for a signal strength positioning system to operate at afrequency chosen so that a corresponding wavelength is longer than atypical range for a relevant propagation environment.

In a typical office or industrial environment, signals are bound byconducting planes in the floor and ceiling like reinforcement rodstructures, metallic pans or metallic sheathing. In this “parallelplate” environment, vertically polarized signals tend to propagatebetter than horizontally polarized signals. In alternate embodiments onemay take advantage of the ability of the propagation environment toshift some energy from one polarization to the other. For instance, ahorizontally polarized transmit signal may couple to a propagationenvironment resulting in adequate vertical polarized energy to bedetected by a vertically polarized receive system.

FIG. 3B is a graphic representation of electric and magnetic field phaserelationships as a function of range for an ideal electrically smallloop in free space. FIG. 3B includes a magnetic or H-Field phase curve397, an electric or E-Field phase curve 398 and a phase difference or Δφcurve 399 representing the difference between curves 397, 398. Curves397, 398, 399 are plotted against a first axis 395 representing phase(preferably in degrees) as a function of range represented on a secondaxis 396 in wavelength (preferably in a kilogram-meter-second unit, suchas meters) of an electromagnetic signal under consideration. H-fieldphase curve 397 begins 90° out of phase with respect to E-field phase398. As range is increased from about 0.05λ to about 0.50λ, H-fieldphase curve 397 initially decreases, and then increases. Similarly, asrange is increased from about 0.05λ to about 0.50λ, E-field phase curve398 increases, gradually at first, and at an increasing rate as rangeincreases. The difference between E-field phase curve 398 and H-fieldphase curve 397 is represented by Δφ curve 399. Δφ curve 399 begins atapproximately 90° (i.e., at phase quadrature) in the near-field within arange of about 0.05λ and goes to 0° (i.e., phase synchronicity) as thefar-field is approached, past a range of about 0.50λ. Transition of Δφcurve 399 from phase quadrature to phase synchronicity between about0.05λ to about 0.50λ is substantially continuous and predictable and isused to advantage by the present invention. With more precisemeasurement, this phase transition can be beneficially used at rangesinside 0.05λ and outside 0.50λ to 1.0λ or more. Further detailsregarding the use of phase in near field location systems may be foundin U.S. patent application Ser. No. 10/355,612, titled “System andMethod for Near-Field Electromagnetic Ranging,” filed Jan. 31, 2003, bySchantz et al., now U.S. Pat. No. 6,963,301, issued Nov. 8, 2005, whichhas been incorporated herein by reference. Thus, in accordance with thepresent invention near field signal propagation properties as evidencedby, for example, amplitude or phase or relative amplitude or relativephase or other characteristics, may be used to determine a location.Near field properties may be used in combination with far fieldproperties to extend the range of a location system.

FIG. 4 is a schematic diagram describing orientation and antennapatterns of a radio frequency (RF) tracking device 400. RF trackingdevice 400 comprises first magnetic antenna 404, second magnetic antenna408, and RF module 412. RF module 412 may be a transmitter, a receiver,or a transceiver. RF module 412 may further include additional modulesuseful for RF tracking device 400. First magnetic antenna 404 has afirst pattern 406 generally aligned along first pattern axis 407 andwith a null generally aligned along first null axis 405. Second magneticantenna 408 has a second pattern 410 generally aligned along secondpattern axis 411 and with a null generally aligned along second nullaxis 409. First pattern axis 407 is substantially orthogonal to secondpattern axis 411. Similarly, first null axis 405 is substantiallyorthogonal to second null axis 409. First pattern axis 407, secondpattern axis 411, first null axis 405 and second null axis 409 liesubstantially within and define an azimuthal or horizontal plane. Firstpattern 406 and second pattern 410 are both substantially verticallypolarized patterns in the vicinity of the azimuthal plane. Thus firstpattern 406 and second pattern 410 jointly provide full verticalpolarization coverage of the azimuthal plane. In a preferred embodiment,first magnetic antenna 404 and second magnetic antenna 408 are loopstickantennas. In alternate embodiments first magnetic antenna 404 and secondmagnetic antenna 208 may be loop antennas or other magnetic antennas.First magnetic antenna 404 and second magnetic antenna 408 are arranged“orthogonally” in that their corresponding null axes (first null axis405 and second null axis 409) are substantially orthogonal to eachother.

FIG. 5 is a schematic diagram describing a first embodiment of an RFtracking device 500, utilizing parallel and perpendicular magneticantennas. FIG. 5 illustrates one configuration of the elements of FIG.4. The RF module 412 is shown generally as a rectangle havingcharacteristic physical dimensions, length, width, and height andassociated axes. Although a rectangle is shown, any shape, as may bedesired for commercial appearance or as needed for other reasons, may beused. First embodiment of RF tracking device 500 comprises firstmagnetic antenna 404, second magnetic antenna 408, and RF module 412.First magnetic antenna 404 is generally aligned with a null along firstnull axis 405 and second magnetic antenna 408 is generally aligned alongsecond null axis 409. First null axis 405 and second null axis 409 aresubstantially orthogonal to each other. First null axis 405 is alsosubstantially co-parallel with normal 505 to RF module 412. First nullaxis 405 and second null axis 409 lie substantially within an azimuthalplane whose normal is vertical axis 507. Thus, first magnetic antenna404 and second magnetic antenna 408 can cooperate to yield substantiallyvertically polarized patterns in the vicinity of the azimuthal plane aswill be further disclosed in this document. Throughout, it should beunderstood that terms like vertical are meant for purposes ofdescription and not limitation, and the overall configuration describedfor RF tracking device 500 may be used in a wide variety oforientations.

FIG. 6 is a schematic diagram showing second embodiment of an RFtracking device 600 utilizing diagonally oriented magnetic antennas.FIG. 6 illustrates an alternate configuration of the elements of FIG. 4.Second embodiment of a RF tracking device 600 comprises first magneticantenna 404, second magnetic antenna 408, and RF module 412. Firstmagnetic antenna 404 is generally aligned with a null along first nullaxis 405 and second magnetic antenna 408 is generally aligned alongsecond null axis 409. First null axis 405 and second null axis 409 aresubstantially orthogonal to each other. First null axis 405 is alsooriented at a diagonal angle of approximately 45 degrees with respect tonormal 505 of RF module 412. Such an orientation yields a compact formfactor for RF tracking device 600. The 45 degree angle shown isexemplary. Other angles may be used, and the particular angle chosen maydepend on the actual shape of the RF module 412 among other factors.Here again, first magnetic antenna 404 and second magnetic antenna 408can cooperate to yield substantially vertically polarized patterns inthe vicinity of the azimuthal plane.

FIG. 7A is a schematic diagram describing a preferred embodiment RFtracking device 700 utilizing multiple diagonal magnetic antennaelements. The use of diagonal antennas reduces package size; the use ofmultiple diagonal antenna elements further improves package size andform factor by reducing the maximum dimensions of the package andeliminating protrusions. In alternate embodiment, multiple antennaelements may be used in the non-diagonal arrangement of FIG. 5.Referring to FIG. 7A, preferred embodiment RF tracking device 700comprises first magnetic antenna system 704, second magnetic antennasystem 708, and RF module 412. The system of FIG. 7A corresponds to thesystem of FIG. 4, with alternate antenna system 704 corresponding toantenna 404 of FIG. 4 and antenna system 708 corresponding to antenna408 of FIG. 4. First magnetic antenna system 704 is generally alignedwith a null along first null axis 405 and second magnetic antenna system708 is generally aligned along second null axis 409. First null axis 405and second null axis 409 are substantially orthogonal to each other.First null axis 405 is also oriented at approximately 45 degrees withrespect to normal 505 of RF module 412.

First magnetic antenna system 704 further comprises first magneticantenna component 713, second magnetic antenna component 714, thirdmagnetic antenna component 715, and fourth magnetic antenna component716 (collectively, “first set of magnetic antenna components”). A firstset of magnetic antenna components are all generally aligned so as tohave nulls generally along first null axis 405 and constructive additionof patterns generally along first pattern axis 407. First magneticantenna system 704 is depicted as having four components for purpose ofillustration and not limitation. In alternate embodiments, firstmagnetic antenna system 704 may further comprise more than fourcomponents or less than four components.

Second magnetic antenna system 708 further comprises fifth magneticantenna component 717, sixth magnetic antenna component 718, seventhmagnetic antenna component 719, and eighth magnetic antenna component720 (collectively, “second set of magnetic antenna components”). Asecond set of magnetic antenna components are all generally aligned soas to have nulls generally along second null axis 409 and constructiveaddition of patterns generally along second pattern axis 411. Secondmagnetic antenna system 708 is depicted as having four components forpurpose of illustration and not limitation. In alternate embodiments,second magnetic antenna system 708 may further comprise more than fourcomponents or less than four components. First magnetic antenna system704 and second magnetic antenna system 708 yield a compact form factorfor RF tracking device 700.

FIG. 7B is a circuit diagram describing a first potential circuitimplementation of magnetic antennas for a preferred embodiment RFtracking device 700. First magnetic antenna system 704 further comprisesfirst magnetic antenna component 713, second magnetic antenna component714, third magnetic antenna component 715, fourth magnetic antennacomponent 716, secondary coupling coil 733, and tuning means 732. Tuningmeans 732 may be a variable capacitor, a varactor, a switchedcapacitance bank or any other means by which first magnetic antennasystem 704 may be tuned. Secondary coupling coil 733 cooperates with oneof the magnetic antenna components, such as magnetic antenna component714, to couple signals between first magnetic antenna system 704 and RFmodule 412. Coupling coil terminals 734 provide means by which signalsmay be coupled intermediate RF module 412 and secondary coupling coil733.

First magnetic antenna component 713, second magnetic antenna component714, third magnetic antenna component 715, and fourth magnetic antennacomponent 716 are all generally aligned so as to have constructiveaddition of patterns generally along first pattern axis 407. If amagnetic antenna component were reversed relative to other magneticantenna components, it is possible to achieve an undesired destructivecombination of patterns. From an electrical point of view, firstmagnetic antenna system 704 may be thought of as a series combination offirst magnetic antenna component 713, second magnetic antenna component714, third magnetic antenna component 715, and fourth magnetic antennacomponent 716. In alternate embodiments, parallel or other morecomplicated combinations are possible.

FIG. 7C is a circuit diagram describing a second potential circuitimplementation of magnetic antennas for a preferred embodiment RFtracking device 700. In this second potential circuit implementation,first magnetic antenna system 704 also further comprises first magneticantenna component 713, second magnetic antenna component 714, thirdmagnetic antenna component 715, and fourth magnetic antenna component716, secondary coupling coil 733, and tuning means 732.

In FIG. 7C, the orientation of second magnetic antenna component 714 andfourth magnetic antenna component 716 have been reversed with respect tothe orientation of first magnetic antenna component 713 and thirdmagnetic antenna component 715. However, using an alternate circuitarrangement depicted in FIG. 7C recovers a desired constructivesuperposition of patterns.

FIG. 8 is a schematic diagram presenting a slanted loopstick antenna804. Slanted loopstick antenna 804 comprises slanted primary coil 831,secondary coupling coil 833 and tuning means 832. Slanted primary coil831 is generally aligned with loopstick axis 805. Loopstick axis 805 isthe rotational axis of a coil form which may be used to form the slantedprimary coil 831. (The coil form itself is optional or may be removedafter forming the coil.) Slanted primary coil 831 comprises turnssubstantially centered with loopstick axis 805 yet oriented so that turnnormal 836 is aligned at an angle φ with respect to loopstick axis 805.“Turn normal 836” refers to an axis normal to a plane substantiallycontaining the turn. Orienting turn normal 836 at an angle φ withrespect to loopstick axis 805 shifts null axis 409 so as to orient thenull axis 409 parallel to turn normal 836 at an angle φ with respect toloopstick axis 805. Similarly, pattern axis 407 remains orthogonal tonull axis 409. Thus slanted loopstick 804 has pattern axis 407 no longersubstantially orthogonal to loopstick axis 805.

In alternate embodiments, slanted loopstick antenna may further comprisea ferrite rod (not shown), however a ferrite rod collinear with theloopstick axis 805 may tend to create a potentially undesired shift ofpattern axis 407 toward loopstick axis 805. A ferrite rod will have thepotentially advantageous effect of increasing inductance and decreasingvulnerability to undesired coupling, such as to nearby objects.

FIG. 9 is a schematic diagram describing a slanted loopstick RF trackingdevice 900. Slanted loopstick RF tracking device 900 comprises firstslanted loopstick 804, second slanted loopstick 908, and RF module 412.First slanted loopstick 804 is constructed so as to align first patternaxis 407 at an angle 90−φ degrees with respect to normal 905 to RFmodule 412. The angle φ may be, for example, 45 degrees. First patternaxis 407 and first pattern null 836 lie substantially within a firstazimuthal plane. Second slanted loopstick 908 is constructed so as toalign second pattern axis 911 at an angle φ degrees with respect tonormal 905. Second pattern axis 911 and second pattern null 936 liesubstantially within a second azimuthal plane parallel to the firstazimuthal plane. Because the two azimuthal planes and respectiveloopstick antennas 804,908 are separated by a small distance relative tothe typical ranging distance for the device 900 in use, the two antennas804, 908 respond essentially as coplanar antennas. Thus, first slantedloopstick 804 and second slanted loopstick 908 have generally orthogonalpatterns that, in combination, can provide full vertical polarizationcoverage for objects near either of the azimuthal planes.

FIG. 10A is a schematic diagram depicting a first configuration of abody mounted electric field antenna. Positioning system antennas may besubject to undesired coupling to nearby objects, resulting in undesiredamplitude and/or phase signal measurements further resulting in positionmeasurement errors. In body mounted systems for tracking people, bodycoupling can result in significant errors. Body coupling can beminimized by including antennas in accordance with the presentinvention.

A first configuration of a body mounted electric field antenna comprisesmonopole element 1022 driven against helmet counterpoise 1021.Alternatively, this arrangement may be thought of as a dipole comprisingmonopole element 1022 as one element and helmet counterpoise 1021 asanother element. First configuration of a body mounted electric fieldantenna avoids undesired coupling to human body 1023 by placing monopoleelement 1022 and helmet counterpoise 1021 relatively far away from humanbody 1023. RF module 412 may be carried on human body 1023 whereverconvenient.

FIG. 10B is a schematic diagram depicting a second configuration of abody mounted electric field antenna. The second configuration of a bodymounted electric field antenna comprises a first dipole element 1024driven against a second dipole element 1025. Second configuration of abody mounted electric field antenna avoids undesired coupling to thehuman body 1023 by enclosing the human body 1023 substantially withinthe first dipole element 1024 and the second dipole element 1025. RFmodule 412 may be carried on the human body 1023 wherever convenient.The first dipole element 1024 and the second dipole element 1025 may beembedded in clothing such as a shirt or coat. In alternate embodiments,the first dipole element 1024 may be embedded in pants and second dipoleelement 1025 may be embedded in a shirt or coat.

FIG. 10C is a schematic diagram showing a potential configuration of abody mounted magnetic field antenna system. A body mounted magneticfield antenna system comprises first magnetic antenna 1004 and secondmagnetic antenna 1008. First magnetic antenna 1004 is generally alignedwith a null along first null axis 405 and second magnetic antenna 1008is generally aligned along second null axis 409. First null axis 405 issubstantially orthogonal to second null axis 409. First null axis 405and second null axis 409 lie substantially within a common azimuthalplane. A body mounted magnetic field antenna system providesomni-directional vertical polarization coverage throughout an azimuthalplane. An advantage of a magnetic field antenna is that a magnetic fieldantenna is less likely to have undesired body coupling. A preferredlocation for body mounted magnetic field antennas is in proximity to awearer's shoulders, away as much as practical from any ferromagneticmaterials such as a steel tank, such as an air tank as typically worn bya fire fighter or hazardous materials worker.

A single magnetic field antenna positioned to accept verticallypolarized signals will not be omni-directional in a horizontal plane.Omnidirectional coverage may be achieved by utilizing multiplevertically polarized magnetic antennas in accordance with the presentinvention. RF module 412 may be carried on human body 1023 whereverconvenient.

FIG. 11 is a schematic diagram describing a potential configuration of acanine magnetic field antenna system 1100. Canine magnetic field antennasystem 1100 comprises a first magnetic antenna 404, and a secondmagnetic antenna 408 embedded in a collar 1127. In alternateembodiments, the collar 1127 may be a harness or other structure thatfastens to a dog 1126 or other animal. The first magnetic antenna 404 isgenerally aligned with a null along the first null axis 405 and thesecond magnetic antenna 408 is generally aligned with the null along thesecond null axis 409. The first null axis 405 is substantiallyorthogonal to the second null axis 409. In still further embodiments,the canine magnetic field antenna system 1100 may be supplemented by athird magnetic antenna 1128 generally oriented so as to align a nullwith a third null axis 1129. The third null axis 1129 is generallyaligned so as to be mutually orthogonal with both the first null axis405 and the second null axis 409. In conjunction with RF module 412,canine magnetic field antenna system 1100 contributes to a system fortracking and monitoring the whereabouts of the dog 1126. Although in apreferred embodiment canine magnetic field antenna system 1100 ismounted on the dog 1126, in alternate embodiments the canine magneticfield antenna system may be employed with a cat, horse, cow, or otherdomestic or wild animal whose whereabouts are of interest. Caninemagnetic field antenna system 1100 may be part of a system that monitorsthe location of an animal and emits noises or electric shocks as adeterrent if an animal attempts to leave a defined safe area or enter adefined prohibited area. In one embodiment, a prohibited area may bedefined using another mobile tracking unit. Thus prohibited areas may bedynamically changing. For example, a prohibited area for a first dog maybe defined as being a predefined two meter radius from a person or a onemeter radius from a second dog. In operation, the first dog could beprohibited from coming closer than the predefined radius from the personor second dog, even though the person or second dog may move around. Thethree antenna configuration of the canine magnetic field antenna system1100 may be advantageously used in any context in which orientation of atag may be arbitrary.

FIG. 12 illustrates one embodiment of a positioning system including aforklift. Forklift positioning system 1200 may include one or more of afirst magnetic antenna 404, a second magnetic 408, and/or an electricantenna 1222. First magnetic antenna 404 is generally aligned with anull along first null axis 405 and second magnetic antenna 408 isgenerally aligned along second null axis 409. First null axis 405 issubstantially orthogonal to second null axis 409. Electric antenna 1222may be a dipole, but is preferentially a monopole element driven againstcounterpoise 1221, which may be the top of the forklift 1227 as shown.RF module 412 may be mounted wherever convenient. In one embodiment, theforklift positioning system 1200 may comprise the first magnetic antenna404 and the second magnetic antenna 408. In another embodiment, theforklift antenna system 1200 may comprise the electric antenna 1222. Instill a further embodiment, the forklift antenna system 1200 maycomprise the first magnetic antenna 404, the second magnetic antenna408, and the electric antenna 1222.

FIG. 13 is a schematic diagram depicting a potential configuration of apallet magnetic field antenna system 1300. Pallet magnetic field antennasystem 1300 comprises first magnetic antenna 404, and second magneticantenna 408 embedded in pallet 1327. In alternate embodiments, pallet1327 may be a box, bin, carton, or other container of assets, such asasset 1326, whose whereabouts are of interest. First magnetic antenna404 is generally aligned with a null along first null axis 405 andsecond magnetic antenna 408 is generally aligned along second null axis409. First null axis 405 is substantially orthogonal to second null axis409.

FIG. 14 is a process flow diagram of a positioning system employing adual magnetic transmit antenna configuration in accordance with thepresent invention. Magnetic antenna system transmission process 1400begins at a START locus 1437.

The dual magnetic transmit antenna positioning process 1400 continueswith the step of, in no particular order, (1) a first transmittergenerating a first signal as indicated in block 1441 and a firstmagnetic antenna radiating the first signal as indicated in block 1439,and (2) a second transmitter generating a second signal as indicated inblock 1442 and a second magnetic antenna radiating the second signal asindicated in block 1440.

In a preferred embodiment, the first magnetic antenna and the secondmagnetic are aligned so as to have substantially orthogonal patterns.Also in a preferred embodiment, the first signal (I) and a second signal(Q) are in quadrature (i.e. a ninety degree phase shift with respect toeach other). In an alternative embodiment, the first signal and secondsignal are transmitted alternately, one at a time at a predeterminedrate or according to a predetermined pattern. If the first signal andthe second signal alternate on a time scale short with respect to thereceiver response time scale (i.e. the receiver averages multipletransmissions), then magnetic antenna system transmission process 1400can achieve an effective omnidirectional vertical polarization radiationpattern, i.e., the system response is substantially the same for anyazimuth angle. Thus, the dual magnetic antenna configuration, whendriven in accordance with the present invention, can result in theequivalent of a substantially omnidirectional response pattern.

The dual transmit antenna positioning process 1400 continues with thestep of a receiver measuring at least one signal characteristic asdenoted in block 1443. At least one signal characteristic may include anamplitude of a signal or a phase of a signal. In alternate embodiments,at least one signal characteristic may include an amplitude or a phaseof an electric signal or a magnetic signal. An electric signal is asignal received by an electric antenna like a monopole, a dipole, or awhip, while a magnetic signal is a signal received by a magnetic antennalike a loop or a loopstick.

The dual transmit antenna positioning process 1400 continues with thestep of a microprocessor determining transmitter position using at leastone signal characteristic as indicated in block 1446. The dual transmitantenna positioning process 1400 terminates at an END locus 1447.

FIG. 15 is a process flow diagram of a dual receive antenna positioningprocess. The process 1500 begins at a START locus 1537, and continueswith the step of a transmitter transmitting a transmitted signal asindicated in block 1538.

The process 1500 continues with the step of, in no particular order, (1)a first magnetic antenna receiving the transmitted signal to generate afirst received signal, as indicated in block 1539, and (2) a secondmagnetic antenna receiving the transmitted signal to generate a secondreceived signal, as indicated in block 1540. The process 1500 continueswith the step of a receiver determining at least one signalcharacteristic from the first and second received signals, as shown inblock 1543.

The dual receive antenna positioning process 1500 continues with thestep of a microprocessor determining transmitter position using thesignal characteristic. The signal characteristic may include anamplitude of a signal or a phase of a signal. In alternate embodiments,the signal characteristic may include an amplitude or a phase of anelectric signal or a magnetic signal. An electric signal is a signalreceived by an electric antenna like a monopole, a dipole, or a whip,while a magnetic signal is a signal received by a magnetic antenna likea loop or a loopstick. The process 1500 terminates at an END locus 1547.

FIG. 16 is a block diagram showing a preferred embodiment magneticantenna transmission system 1600 for use in a positioning system.Magnetic antenna transmission system 1600 comprises oscillator 1649,divide by two divider 1650, XOR gate 1651, first power amplifier 1652,second power amplifier 1653, first magnetic antenna 1604, and secondmagnetic antenna 1608. In a preferred embodiment, first magnetic antenna1604, and second magnetic antenna 1608 are arranged orthogonally.Transmitter system 1648 comprises oscillator 1649, divide by two divider1650, XOR gate 1651, first power amplifier 1652, and second poweramplifier 1653. Transmitter system 1648 is an example of an RF module,such as RF module 412.

Oscillator 1649 operates at twice a desired frequency f to yield a clocksignal C. Divide by two divider 1650 takes clock signal C at frequency2f and divides it by two to yield an in-phase signal I at frequency fXOR gate 1651 accepts clock signal C as a first input and in-phasesignal I as a second input. XOR gate 1651 yields quadrature outputsignal Q. Quadrature output signal Q is shifted ninety degrees withrespect to in-phase signal I. First power amplifier 1652 amplifiesin-phase signal I and conveys it to first magnetic antenna 1604. Secondpower amplifier 1653 amplifies quadrature signal Q and conveys it tosecond magnetic antenna 1608. Feeding a first in-phase signal I to firstmagnetic antenna 1604 and a second quadrature signal Q to secondmagnetic antenna 1608 enables a preferred embodiment magnetic antennatransmission system 1600 to radiate substantially omnidirectionalvertically polarized electromagnetic waves.

First power amplifier 1652 and second power amplifier 1653 may furtherinclude filtering means, matching means, or power control means.Filtering means include high pass, low pass, band pass or band notchfilters such as are generally understood by practitioners of the RFarts. Filtering means enable first power amplifier 1652 and second poweramplifier 1653 to deliver appropriate frequency components to firstmagnetic antenna 1604 and second magnetic antenna 1608. Matching meansinclude impedance transformation and balun transformation. Power controlmeans allow output power of first power amplifier 1652 and second poweramplifier 1653 to be adjusted so as to meet a desired powerspecification such as one imposed by a regulatory limit.

Preferred embodiment magnetic antenna transmission system 1600 isparticularly useful for a positioning system operating at relatively lowfrequencies such as those less than 2 MHz. At relatively low frequenciesit is relatively easy to generate a clock signal at twice a frequency ofinterest. The inventors have successfully used direct digital synthesis.A variety of other techniques are possible including other digitaltechniques, quartz oscillators, multi-vibrators, synthesizers, LCoscillators and other oscillators. At higher frequencies it becomes moredifficult to generate a clock signal at twice a frequency of interest.For these higher frequencies, alternate embodiments using a clock oroscillator operating at the frequency of interest become moreattractive.

FIG. 17A is a timing diagram showing a typical clock signal 1654 in apreferred embodiment magnetic antenna transmission system. Clock signal1654 toggles at a frequency 2f for a magnetic antenna transmissionsystem 1600 where transmission at a frequency f is desired. In anexemplary system, divide by two divider 1650 triggers on a falling edgesuch as falling edge 1655.

FIG. 17B is a timing diagram showing a typical in-phase (I) signal 1656in a preferred embodiment magnetic antenna transmission system 1600.In-phase (I) signal 1656 toggles at frequency f.

FIG. 17C is a timing diagram showing a typical quadrature (Q) signal1657 in a preferred embodiment magnetic antenna transmission system1600. Quadrature (Q) signal 1657 toggles at frequency f and is shiftedin time by a quarter period with respect to in-phase (I) signal 1656.

FIG. 18 is a block diagram showing a first alternate embodiment magneticantenna transmission system 1800 for use in a positioning system. Firstalternate embodiment magnetic antenna transmission system 1800 comprisesoscillator 1849, quadrature splitter 1858, first power amplifier 1852,second power amplifier 1853, first magnetic antenna 1804, and secondmagnetic antenna 1808. In a preferred embodiment, first magnetic antenna1804, and second magnetic antenna 1808 are arranged orthogonally.Transmitter system 1848 comprises oscillator 1849, quadrature splitter1858, first power amplifier 1852, and second power amplifier 1853.Transmitter system 1848 is an example of an RF module, such as RF module412.

Oscillator 1849 generates a sine wave signal at a frequency f andconveys a sine wave signal to a quadrature splitter 1858. Quadraturesplitter 1858 yields a first in-phase signal I and a second quadraturesignal Q. First power amplifier 1852 amplifies a first in-phase signal Iand delivers a first in-phase signal I to first magnetic antenna 1804.Second power amplifier 1853 amplifies a second quadrature signal Q anddelivers a second quadrature signal Q to second magnetic antenna 1808.Feeding a first in-phase signal I to first magnetic antenna 1804 and asecond quadrature signal Q to second magnetic antenna 1808 enables afirst alternate embodiment magnetic antenna transmission system 1800 toradiate substantially omnidirectional vertically polarizedelectromagnetic waves.

The main advantage of first alternate embodiment magnetic antennatransmission system 1800 is that it does not require any operation atfrequencies higher than a preferred frequency f. This makes firstalternate embodiment magnetic antenna transmission system 1800 suitablefor use at higher frequencies, such as 13.56 MHz, where it becomes moredifficult to implement the digital approach of preferred embodimentmagnetic antenna transmission system 1600.

FIG. 19 is a block diagram showing a second alternate embodimentmagnetic antenna transmission system 1900 for use in a positioningsystem. Second alternate embodiment magnetic antenna transmission system1900 comprises oscillator 1949, switch 1959, first power amplifier 1952,second power amplifier 1953, first magnetic antenna 1904, and secondmagnetic antenna 1908. Transmitter system 1948 comprises oscillator1949, switch 1959, first power amplifier 1952, and second poweramplifier 1953. Transmitter system 1948 is an example of an RF module,such as RF module 412.

Switch 1959 toggles back and forth on a time scale short with respect toa receiver average response time scale. In a preferred embodiment, firstmagnetic antenna 1904, and second magnetic antenna 1908 are arrangedorthogonally. Thus, second alternate embodiment magnetic antennatransmission system 1900 can achieve an effective omnidirectionalvertical polarization radiation pattern. Thus, second alternateembodiment magnetic antenna transmission system 1900 radiateseffectively omnidirectional vertically polarized electromagnetic waves.In an alternate embodiment, switch 1959 may switch at anotherpredetermined rate or pattern, such as a rate longer than thereceiceiver average response time scale.

Thus the two magnetic antennas may be used to transmit the equivalent ofan omnidirectional pattern by driving the antennas in an orthogonalmanner. The orthogonal drive may be, for example, time orthogonal asshown in the switched antenna examples, or phase orthogonal as shown inthe phase quadrature examples. Other orthogonal switching patterns orsignals may also be used. Since one objective of the orthogonalsignaling is to provide coverage in the null of one antenna, strictorthogonality may not be necessary, an adequate component oforthogonality to overcome the deep null of one antenna may besufficient.

Orthogonal drive may be in addition to the orthogonal arrangement of thenull patterns of the two antennas. As with the drive, strictorthogonality of the antenna null patterns may not be necessary for allapplications. Packaging constraints or other considerations may dictatea less than perfect implementation. Thus, in a further embodiment, thenull axes are arranged with a 60 degree separation. In a furtherembodiment, three antennas may be arranged with nulls at 0, 60 and 120degrees and driven with time orthogonal signals, or with three phasesignals substantially at 0, 120 and 240 degree phase angles. Additionalarrays of multiple antennas may be extrapolated from this teaching.

FIG. 20 is a block diagram showing a preferred embodiment magneticantenna reception system 2000 for use in a positioning system. Magneticantenna reception system 2000 comprises first magnetic antenna 2004,second magnetic antenna 2008, first receiver 2061, second receiver 2062,first signal strength detector 2063, second signal strength detector2065, microprocessor 2066, and in some embodiments, phase comparator2064. In a preferred embodiment, first magnetic antenna 2004, and secondmagnetic antenna 2008 are arranged orthogonally. Receiver system 2012comprises first receiver 2061, second receiver 2062, first signalstrength detector 2063, second signal strength detector 2065, and insome embodiments, phase comparator 2064. Receiver system 2012 is anexample of an RF module, such as RF module 412.

The microprocessor 2066 typically determines a received power bycombining received power information from the first magnetic antenna2004 and the second magnetic antenna 2008. In one embodiment, the powerlevels detected in the two antennas 2004, 2008 are summed. In anotherembodiment, the ratio of the power levels is used to determine a powermultiplier factor based on the antenna receive patterns. The powermultiplier is then applied to the greater power of the two to determineactual received power.

FIG. 21 is a block diagram showing a mobile locator tag 2180 for use ina positioning system. Mobile locator tag 2180 comprises first magneticantenna 2104, second magnetic antenna 2108, RF module 2112, electricantenna 2167, transceiver 2170, microprocessor 2166, alternate trackinginterface 2172, user interface 2171, sensor interface 2173, first sensor2176, second sensor 2177, third sensor 2178, nth sensor 2179, andcommunications interface 2174. The sensors 2173, 2176, 2177, and 2179may be collectively referred to as a sensor net. Mobile locator tag 2180receives signals from fixed beacon transmitters like fixed beacontransmitter 2281 and communicates with a local data center 2175.

RF module 2112 is a near field receiver comprising a first receiver 2169and a second receiver 2168. First receiver 2169 detects signals from afirst magnetic antenna 2104, and second receiver 2168 detects signalsfrom a second magnetic antenna 2108. In a preferred embodiment, firstmagnetic antenna 2104 and second magnetic antenna 2108 are arrangedorthogonally. First receiver 2169 and second receiver 2168 may useanalog or digital techniques for determining signal properties such asRSSI. For instance, first receiver 2169 and second receiver 2168 mayperform a Fourier Transform operation like an FFT on a received timedomain waveform to simultaneously identify amplitude and phasecharacteristics of multiple near field signals at various frequencies.RF module 2112 communicates signal characteristics to microprocessor2166. Microprocessor 2166 conveys command and control signals to RFmodule 2112.

Near field transceiver 2170 receives signals from electric field antenna2167. Electric field antenna detects electric field signals from fixedbeacon transmitter 2281. In alternate embodiments, near fieldtransceiver 2170 can also transmit data signals to fixed beacontransmitter 2281 intermediate electric field antenna 2167.Microprocessor 2166 conveys command and control signals as well as datasignals to near field transceiver 2170.

An optional alternate tracking interface 2172 conveys data intermediatea microprocessor and an alternate tracking system. For instance, a shortrange high precision tracking system such as a UWB, IR, acoustic, orshort range near field electromagnetic positioning system may beemployed to perform supplemental or ancillary positioning and trackingof other mobile-locator receivers in the immediate vicinity.Microprocessor 2166 conveys command and control signals to alternatetracking interface 2172 and receives data pertaining to location andposition.

A particularly useful alternate tracking system is a near fieldamplitude positioning system operating at frequencies in the vicinity of13.56 MHz with a wavelength (λ=22 m). Such a frequency is suitable forprecision near field amplitude positioning to a range of 3-10 m. A nearfield amplitude positioning system at 13.56 MHz is particularly wellsuited for monitoring people within a small unit, or squad. A near fieldamplitude positioning system operating at frequencies in the vicinity of13.56 MHz is also suitable as a stand-alone system for monitoring socialinteractions and contacts between people in a residential or officeenvironment. In such an application, a mobile transmitter tag co-locatedwith a mobile locator receiver tag facilitates mutual ranging andpositioning.

Optional user interface 2171 provides means to control mobile locatortag 2180 and obtain information from mobile locator tag 2180. Userinterface 2171 conveys command and control signals to microprocessor2166 and provides means for accessing information stored inmicroprocessor 2166. Optional user interface 2171 may employ visual,audio or tactile means of conveying data to a user. Optional userinterface 2171 may further comprise means for a user to control a mobilelocator tag or otherwise input relevant data to a microprocessor.

Microprocessor 2166 includes input/output capability, memory and/or datastorage capability, and processing capability. Preferentially,microprocessor 2166 also includes the ability to monitor data fromsensor interface 2173, apply rules, and react to data from sensorinterface 2173. Microprocessor 2166 can convey data, alarms, alerts, orstatus information via communications interface 2174 to a local datacenter 2175. In some embodiments, microprocessor 2166 can store andallow retrieval of other information including for instance invoices,bills of lading, material safety data, and sensor logs.

Sensor interface 2173 may exchange control and data signals with thesensor net. Sensor interface 2173 may include wired or wireless links tothe sensor net. Sensor interface 2173 is preferentially compatible withIEEE 1451.2 or similar such protocols for data exchange. Preferentially,sensor interface 2173 enables a modular approach to sensor net 2173 inwhich a wide variety of sensors may be selected to fulfill a variety ofdesired missions, including container security, container surveillance,container integrity, and container safety.

Sensor interface 2173 may connect to a variety of sensors. For purposesof illustration and not limitation, first sensor 2176 might detect heartrate, body temperature, respiration or other vital statistic of anindividual associated with mobile locator tag 2180. Alternatively, firstsensor 2176 might detect oxygen tank level, battery status, orammunition level status of an individual associated with mobile locatortag 2180. Second sensor 2177 might detect motion and thus be able todetermine when mobile locator tag 2180 moves and should transmit anupdate. Such a motion detector might be part of a more comprehensiveinertial tracking system that could provide valuable information tocontribute toward an accurate position solution. Third sensor 2178 mightdetect temperature, humidity, the presence of dangerous chemical orbiological agents or the presence of ionizing radiation that mightindicate environmental hazards dangerous for the person or assetassociated with mobile locator tag 2180. As many additional sensors asmight be desired may be added, up to and including an n^(th) sensor 2179that might detect tampering or the presence of undesired activity in thevicinity of a valuable asset. In the context of a positioning system forassets, sensor interface 2173 enables asset integrity and security to bepreserved and also allows early detection of potential hazards or otheranomalies. In the context of a positioning system for people or animals,sensor interface 2173 enables health and safety to be monitored andprovides for prompt detection of potentially hazardous or dangeroussituations. Discussions of specific sensors are for purposes ofillustration not limitation.

Local data center 2175 (LDC) receives and processes data from mobilelocator receiver tags like mobile receiver locator tag 2180. This datamay include signal strength (RSSI) or other signal characteristicsincluding phase characteristics. Local data center 2175 can use datafrom a mobile locator tag 2180 to determine position of a mobile locatortag 2180 using a ranging algorithm with plurality of appropriate rangingparameters for a given propagation environment as selected by a user orother schemes. Alternatively a mobile-locator tag 2180 may performcertain processing locally and convey ranges or a calculated position toa local data center 2175.

Nothing in this description should be interpreted so as to require allelements depicted in FIG. 21. For instance in alternate embodiments,mobile locator receiver tag 2180 may omit alternate tracking interface2172, user interface 2171, sensor interface 2173, first sensor 2176,second sensor 2177, third sensor 2178, nth sensor 2179, orcommunications interface 2174. Mobile locator receiver tag 2180 requiresonly those elements needed for a particular application.

FIG. 22 is a block diagram presenting a fixed beacon transmitter 2281for use in a positioning system. Fixed beacon transmitter 2281 compriseselectric field antenna 2267, near field transceiver 2270, user interface2271, positioning system 2282, microprocessor 2266, sensor interface2273, first sensor 2276, second sensor 2277, third sensor 2278, nthsensor 2279, and communications interface 2274. Fixed beacon transmitter2281 transmits signals to mobile locator receiver tags (like mobilereceiver tag 2180). Fixed beacon transmitter 2281 communicates with alocal data center 2175.

Near field transceiver 2270 transmits a signal via electric fieldantenna 2267 to mobile locator receiver tags, like mobile locatorreceiver tag 2180. In alternate embodiments, near field transceiver 2270can also receive data signals from mobile locator receiver tags, likemobile locator receiver tag 2180, intermediate electric field antenna2267. Microprocessor 2266 conveys command and control signals as well aspotentially receives data signals from near field transceiver 2270.

In alternate embodiments, a near field transceiver 2270 may includemeans for transmitting and receiving near field signals through apropagation environment to other beacon transmitter devices 2270 atknown locations so as to measure appropriate ranging parameters for usein a ranging algorithm.

An optional positioning system 2282 may include use of pre-surveyedlandmarks, GPS, UWB, laser range finding, or near field electromagneticranging to establish location of a fixed beacon transmitter.Microprocessor 2166 conveys command and control signals to optionalpositioning system 2282 and receives data pertaining to location andposition.

Optional user interface 2271 provides means to control fixed beacontransmitter 2281 and obtain information from fixed beacon transmitter2281. User interface 2271 conveys command and control signals tomicroprocessor 2266 and provides means for accessing information storedin microprocessor 2266. Optional user interface 2271 may employ visual,audio or tactile means of conveying data to a user. Optional userinterface 2271 may further comprise means for a user to control a fixedbeacon transmitter 2281 or otherwise input relevant data to amicroprocessor 2266.

Microprocessor 2266 includes input/output capability, memory and/or datastorage capability, and processing capability. Preferentially,microprocessor 2266 also includes the ability to monitor data fromsensor interface 2273, apply rules, and react to data from sensorinterface 2273. Microprocessor 2266 can convey data, alarms, alerts, orstatus information via communications interface 2274 to a local datacenter 2175. Microprocessor 2266 can store and allow retrieval of otherinformation including for instance invoices, bills of lading, materialsafety data, and sensor logs.

Sensor interface 2273 exchanges control and data signals intermediatesensors (such as sensor 2276) and a microprocessor 2266. Sensorinterface 2273 may include wired or wireless links to a sensor net (notshown). Sensor interface 2273 is preferentially compatible with IEEE1451.2 or similar such protocols for data exchange. Preferentially,sensor interface 2273 enables a modular approach to the sensor net inwhich a wide variety of sensors may be selected to fulfill a variety ofdesired missions.

The sensor net may connect to a variety of sensors. For purposes ofillustration and not limitation, first sensor 2276 might detect heartrate, body temperature, respiration or other vital statistic of anindividual associated with mobile locator tag 2280. Alternatively, firstsensor 2276 might detect oxygen tank level, battery status, orammunition level status of an individual associated with mobile locatortag 2280. Second sensor 2277 might detect motion and thus be able todetermine when mobile locator tag 2280 moves and should transmit anupdate. Such a motion detector might be part of a more comprehensiveinertial tracking system that could provide valuable information tocontribute toward an accurate position solution. Third sensor 2278 mightdetect temperature, humidity, the presence of dangerous chemical orbiological agents or the presence of ionizing radiation that mightindicate environmental hazards dangerous for the person or assetassociated with mobile locator tag 2280. As many additional sensors asmight be desired may be added, up to and including an n^(th) sensor 2279that might detect tampering or the presence of undesired activity in thevicinity of a valuable asset. In the context of a positioning system forassets, sensor interface 2273 enables asset integrity and security to bepreserved and also allows early detection of potential hazards or otheranomalies. In the context of a positioning system for people or animals,sensor interface 2273 enables health and safety to be monitored andprovides for prompt detection of potentially hazardous or dangeroussituations. Discussions of specific sensors are for purposes ofillustration not limitation.

Local data center 2175 (LDC) receives and processes data from fixedbeacon transmitters like fixed beacon transmitter 2281. Local datacenter 2175 may also convey command and control signals to fixed beacontransmitter 2281.

Nothing in this description should be interpreted so as to require allelements depicted in FIG. 22. For instance in alternate embodiments,fixed beacon transmitter 2281 may omit positioning system 2282, sensorinterface 2273, first sensor 2276, second sensor 2277, third sensor2278, nth sensor 2279, or communications interface 2174. Fixed beacontransmitter 2281 requires only those elements needed for a particularapplication.

FIG. 23 is a block diagram describing a fixed locator receiver 2383 foruse in a positioning system. Fixed locator receiver 2383 comprises firstmagnetic antenna 2304, second magnetic antenna 2308, RF module 2312,electric antenna 2367, transceiver 2370, microprocessor 2366, alternatetracking interface 2372, user interface 2371, sensor interface 2373,first sensor 2376, second sensor 2377, third sensor 2378, nth sensor2379, and communications interface 2374. Mobile locator tag 2383receives signals from mobile transmitter tags like mobile transmittertag 2484 and communicates with a local data center 2375.

RF module 2312 is a near field receiver comprising first receiver 2369and second receiver 2368. First receiver 2369 detects signals from firstmagnetic antenna 2304, and second receiver 2368 detects signals fromsecond magnetic antenna 2308. In a preferred embodiment, first magneticantenna 2304 and second magnetic antenna 2308 are arranged orthogonally.First receiver 2369 and second receiver 2368 may use analog or digitaltechniques for determining signal properties such as signal strength(RSSI). For instance, first receiver 2369 and second receiver 2368 mayperform a Fourier Transform operation like an FFT on a received timedomain waveform to simultaneously identify amplitude and phasecharacteristics of multiple near field signals at various frequencies.RF module 2312 communicates signal characteristics to microprocessor2366. Microprocessor 2366 conveys command and control signals to RFmodule 2312.

Near field transceiver 2370 receives signals from electric field antenna2367. Electric field antenna 2367 detects electric field signals frommobile transmitter tag 2484. In alternate embodiments, near fieldtransceiver 2370 can also transmit data signals to mobile transmittertag 2484 intermediate electric field antenna 2367. Microprocessor 2366conveys command and control signals as well as data signals to nearfield transceiver 2370.

An optional alternate tracking interface 2372 conveys data intermediatea microprocessor and an alternate tracking system. For instance, a shortrange high precision tracking system such as a UWB, IR, acoustic, orshort range near field electromagnetic positioning system may beemployed to perform supplemental or ancillary positioning and trackingof other mobile-locator receivers in the immediate vicinity.Microprocessor 2366 conveys command and control signals to alternatetracking interface 2372 and receives data pertaining to location andposition.

Optional user interface 2371 provides means to control fixed locatorreceiver 2383 and obtain information from fixed locator receiver 2383.User interface 2371 conveys command and control signals tomicroprocessor 2366 and provides means for accessing information storedin microprocessor 2366. Optional user interface 2371 may employ visual,audio or tactile means of conveying data to a user. Optional userinterface 2371 may further comprise means for a user to control a fixedlocator receiver 2383 or otherwise input relevant data to amicroprocessor 2266.

Microprocessor 2366 includes input/output capability, memory and/or datastorage capability, and processing capability. Preferentially,microprocessor 2366 also includes the ability to monitor data fromsensor interface 2373, apply rules, and react to data from sensorinterface 2373. Microprocessor 2366 can convey data, alarms, alerts, orstatus information via communications interface 2374 to a local datacenter 2375. Microprocessor 2366 can store and allow retrieval of otherinformation including for instance invoices, bills of lading, materialsafety data, and sensor logs.

Sensor interface 2373 exchanges control and data signals intermediate asensor (like sensor 2376) and a microprocessor 2366. Sensor interface2373 may include wired or wireless links to a sensor net (not shown).Sensor interface 2373 is preferentially compatible with IEEE 1451.2 orsimilar such protocols for data exchange. Preferentially, sensorinterface 2373 enables a modular approach to sensor net 2373 in which awide variety of sensors may be selected to fulfill a variety of desiredmissions.

Local data center 2375 receives and processes data from fixed locatorreceivers like fixed locator receiver 2383. This data may include signalstrength (RSSI) or other signal characteristics including phasecharacteristics. Local data center 2375 can use data from fixed locatorreceiver 2383 to determine position of a mobile transmitter tag 2484using a ranging algorithm with plurality of appropriate rangingparameters for a given propagation environment as selected by a user orother schemes. Alternatively a fixed locator receiver 2383 may performcertain processing locally and convey ranges or a calculated position toa local data center 2375.

Nothing in this description should be interpreted so as to require allelements depicted in FIG. 23. For instance in alternate embodiments,fixed locator receiver 2383 may omit alternate tracking interface 2372,user interface 2371, sensor interface 2373, first sensor 2376, secondsensor 2377, third sensor 2378, nth sensor 2379, or communicationsinterface 2374. Mobile locator receiver tag 2380 requires only thoseelements needed for a particular application.

FIG. 24 is a block diagram laying out a mobile transmitter tag 2484 foruse in a positioning system. Mobile transmitter tag 2484 comprises firstmagnetic field antenna 2404, second magnetic field antenna 2408, RFmodule 2412, user interface 2471, alternate tracking interface 2472,microprocessor 2466, sensor interface 2473, first sensor 2476, secondsensor 2477, third sensor 2478, nth sensor 2479, and communicationsinterface 2474. Mobile transmitter tag 2484 transmits signals to fixedlocator receivers (like fixed locator receiver 2383). Mobile transmittertag 2484 also communicates with a local data center 2375.

RF module 2412 comprises transmitter 2448, first power amplifier 2452,and second power amplifier 2453. Preferred embodiment magnetic antennatransmission system 1600, first alternate embodiment magnetic antennatransmission system 1800, and second alternate embodiment magneticantenna transmission system 1900 are potential implementations of RFmodule 2412. RF module 2412 conveys signals to first magnetic antenna1804, and second magnetic antenna 1808. In a preferred embodiment, firstmagnetic antenna 1804, and second magnetic antenna 1808 are arrangedorthogonally.

An optional alternate tracking interface 2472 conveys data intermediatea microprocessor and an alternate tracking system. For instance, a shortrange high precision tracking system such as a UWB, IR, acoustic, orshort range near field electromagnetic positioning system may beemployed to perform supplemental or ancillary positioning and trackingof other mobile-locator receivers in the immediate vicinity.Microprocessor 2466 conveys command and control signals to alternatetracking interface 2472 and receives data pertaining to location andposition.

Microprocessor 2466 includes input/output capability, memory and/or datastorage capability, and processing capability. Preferentially,microprocessor 2466 also includes the ability to monitor data fromsensor interface 2473, apply rules, and react to data from sensorinterface 2473. Microprocessor 2466 can convey data, alarms, alerts, orstatus information via communications interface 2474 to a local datacenter 2375. Microprocessor 2466 can store and allow retrieval of otherinformation including for instance invoices, bills of lading, materialsafety data, and sensor logs.

Sensor interface 2473 exchanges control and data signals intermediatesensor (such as sensor 2476) and a microprocessor 2466. Sensor interface2473 may include wired or wireless links to sensor net. Sensor interface2473 is preferentially compatible with IEEE 1451.2 or similar suchprotocols for data exchange. Preferentially, sensor interface 2473enables a modular approach to sensor net 2473 in which a wide variety ofsensors may be selected to fulfill a variety of desired missions.

Sensor interface 2473 may connect to a variety of sensors. For purposesof illustration and not limitation, first sensor 2476 might detect heartrate, body temperature, respiration or other vital statistic of anindividual associated with mobile transmitter tag 2484. Alternatively,first sensor 2476 might detect oxygen tank level, battery status, orammunition level status of an individual associated with mobiletransmitter tag 2484. Second sensor 2477 might detect motion and thus beable to determine when mobile transmitter tag 2484 moves and shouldtransmit an update. Such a motion detector might be part of a morecomprehensive inertial tracking system that could provide valuableinformation to contribute toward an accurate position solution. Thirdsensor 2478 might detect temperature, humidity, the presence ofdangerous chemical or biological agents or the presence of ionizingradiation that might indicate environmental hazards dangerous for theperson or asset associated with mobile transmitter tag 2484. As manyadditional sensors as might be desired may be added, up to and includingan n^(th) sensor 2479 that might detect tampering or the presence ofundesired activity in the vicinity of a valuable asset. In the contextof a positioning system for assets, sensor interface 2473 enables assetintegrity and security to be preserved and also allows early detectionof potential hazards or other anomalies. In the context of a positioningsystem for people or animals, sensor interface 2473 enables health andsafety to be monitored and provides for prompt detection of potentiallyhazardous or dangerous situations. Discussions of specific sensors arefor purposes of illustration not limitation.

Optional user interface 2471 provides means to control mobiletransmitter tag 2484 and obtain information from mobile transmitter tag2484. User interface 2471 conveys command and control signals tomicroprocessor 2366 and provides means for accessing information storedin microprocessor 2366. Optional user interface 2471 may employ visual,audio or tactile means of conveying data to a user. Optional userinterface 2471 may further comprise means for a user to control a mobiletransmitter tag 2484 or otherwise input relevant data to amicroprocessor 2266.

Local data center 2375 optionally receives and processes data frommobile transmitter tags like mobile transmitter tag 2484. Local datacenter 2375 may also convey command and control signals to mobiletransmitter tag 2484.

Nothing in this description should be interpreted so as to require allelements depicted in FIG. 24. For instance in alternate embodiments,mobile transmitter tag 2484 may omit user interface 2471, alternatetracking interface 2472, sensor interface 2473, first sensor 2476,second sensor 2477, third sensor 2478, nth sensor 2479, andcommunications interface 2474. Mobile transmitter tag 2484 requires onlythose elements needed for a particular application.

Note that the magnetic antennas discussed with reference to FIGS. 16-24and as generally discussed in this disclosure may be a magnetic antennaof any appropriate design. In particular, the magnetic antennas of FIGS.4-8 are well adapted for the applications of FIGS. 16-20.

FIG. 25 illustrates an exemplary indoor deployment of a positioningsystem including fixed locator receivers and mobile transmitter tags. Aplurality of mobile beacon transmitters 2484 are attached to people 623,fixed assets 2587, mobile assets 2588 or other objects whose position isdesired to be known. Fixed locator receivers 2383 are placed at variousknown positions within a building 2585

In accordance with the present invention, ranging may be determinedusing free space equations as illustrated in FIG. 3. The equations maybe adjusted for ground plane effects and potentially for imperfectground plane conductivity. In a further embodiment, complex structures,such as buildings, urban areas, wooded areas, or even specific buildingtypes such as wood frame, concrete block, steel stud or other typicalbuilding types may be evaluated through empirical experiment todetermine typical attenuation or phase shift characteristics. Thecharacteristics may be evaluated over a range of buildings of the sametype to establish an average characteristic. The average characteristicsmay be expressed in the form of standardized equations or standardizedalgorithm so that only a few parameters, such as an exponential decayrate need be specified to establish a range model for a particularsituation.

In another embodiment, a particular locale may be mapped by usingtransmitters and receivers at predetermined locations by transmittingand receiving at a large number of locations within the locale. The mapmay then be stored in a database. In use, readings of signalcharacteristics are taken and compared with the database map todetermine by lookup and/or interpolation, the precise location indicatedby the signal readings. Further details of signal mapping techniques aredisclosed in U.S. patent application Ser. No. 10/958,165, titled “Nearfield electromagnetic positioning system and method,” filed Oct. 4, 2004by Schantz et al and published as Pub. No. 2005/0046608 A1, which isincorporated herein by reference in its entirety.

A local data center (LDC) 2375 receives and processes data from mobilebeacon transmitters 2484 and fixed locator receivers 2383. This data mayinclude RSSI's or other signal characteristics including phasecharacteristics. A local data center (LDC) 2375 can use data from afixed locator receiver 2383 to determine position of a mobile beacontransmitter 2484 using a ranging algorithm with plurality of appropriateranging parameters for a given propagation environment as selected by auser. Alternatively a fixed locator receiver 2383 may perform rangeand/or position processing locally and convey ranges or a calculatedposition to a local data center (LDC) 2375.

FIG. 26 illustrates an exemplary indoor deployment of a positioningsystem including fixed beacon transmitters and mobile locator receivertags. Mobile locator receivers 2180 are attached to people 623, valuableassets 2587, mobile assets 2588 or other objects whose position isdesired to be known. Fixed beacon transmitters 2281 are placed atvarious known positions within a building 2585. A local data center(LDC) 2175 receives data regarding signal characteristics or ranges frommobile locator receivers 2180. In one embodiment, the local data center2175 calculates ranges based on signal characteristic data as receivedby the mobile locator receivers 2180. In an alternate embodiment, themobile locator receivers 2180 perform range calculation and pass rangeinformation to the local data center 2175.

FIG. 27 illustrates an exemplary positioning system including fixedbeacon transmitters and mobile locator receiver tags at an incidentscene as may be used by the military or emergency responders.

The incident scene is a building, facility, or other environmentrequiring an emergency response from emergency responders like police,fire, paramedic, rescue, hazardous material, military, or other suchindividuals. Users deploy beacon transmitters 22811 through 22814 aroundor throughout an incident scene.

Users also select a plurality of appropriate ranging parameters for apropagation algorithm based on the nature of the incident scene. Forinstance, if the incident scene is a multi-resident dwelling, users mayselect a plurality of appropriate ranging parameters for amulti-resident dwelling. If the incident scene is a warehouse, users mayselect a plurality of appropriate ranging parameters for a warehouse. Ifthe incident scene is an office building, users may select a pluralityof appropriate ranging parameters for an office building. Users may beprovided with a menu of options to allow them to select a plurality ofoptimal ranging parameters for a propagation algorithm. A plurality ofranging parameters may include but is not necessarily limited to a slopeand intercept for a linear range vs. RSSI relationship.

FIG. 27 shows four beacon transmitters 22811 through 22814 for purposesof illustration. Additional beacon transmitters may yield a larger zoneof coverage and/or a more accurate solution. Fewer beacon transmittersmay yield a less accurate but still potentially useful positionsolution. Beacon transmitters 22811 through 22814 may be stand aloneunits or mounted on vehicles 2789. Beacon transmitters 22811 through22814 may employ an alternate positioning system 2282 like pre-surveyedlandmarks, GPS, UWB, laser range finding, or near field electromagneticranging to establish their locations via alternate positioning system.Beacon transmitters 22811 through 22814 may also include a transceivercapability to convey data intermediate mobile locator receiver tags 2180and a local data center (LDC) 2175.

Preferably the beacon transmitters 22811 through 22814 should emit anear field signal of constant power. Regulated transmit power controlmeans can help ensure a constant transmit power. Power level mayalternatively be adjusted to maintain constant received power inresponse to variations in path attenuation, which may include variationsin orientation of mobile units.

Alternatively, received power RSSI measurements may be adjusted tocompensate for variations in transmitted power, which may vary as afunction of battery levels and other factors.

The operation of one embodiment of the system will now be described indetail with reference to FIG. 27. The positions of the beacontransmitters 22811 through 22814 may be determined by survey or by GPSor by other methods that may be suitable for use outside the buildingbut may not be suitable for use inside the building. When the positionsof the beacon transmitters 22811 through 22814 are known, the system maycommence operation. A mobile locator receiver tag 2180 receives a firstsignal from a first beacon transmitter 22811 and determines a firstRSSI. The mobile locator receiver tag 2180 receives a second signal froma second beacon transmitter 22812 and determines a second RSSI. Themobile locator receiver tag 2180 receives a third signal from a thirdbeacon transmitter 22813 and determines a third RSSI. The mobile locatorreceiver tag 2180 receives a fourth signal from a fourth beacontransmitter 22814 and determines a fourth RSSI. Using a plurality ofranging parameters suitable for the incident scene, the mobile locatorreceiver tag 2180 determines ranges (R1 through R4) to each respectivebeacon transmitter. Ranges R1 through R4 may be used by a mobile locatorreceiver tag 2180 to determine position using multilateration or othertechniques. Alternatively, a mobile locator receiver tag 2180 may conveyranges R1 through R4 to a local data center 2175 where position may bedetermined.

The local data center 2175 receives and processes data from beacontransmitters 22811 through 22814 and mobile locator receiver tag 2180.This data includes RSSI's or other signal characteristics includingphase characteristics. The local data center 2175 can use data from amobile locator receiver tag 2180 to determine position of a mobilelocator receiver tag 2180 using a ranging algorithm with plurality ofappropriate ranging parameters for a given propagation environment asselected by a user. Alternatively the mobile-locator receiver tag 2180may perform range and/or position calculation processing locally andconvey ranges or calculated position to a local data center 2175.

In alternate embodiments, appropriate ranging parameters for a givenpropagation environment may be determined for a particular incidentscene by a plurality of beacon transmitters 22811 through 22814 sendingsignals through the incident scene propagation environment to locatorreceivers 2180 at known positions (not shown), for instance, co-locatedwith other beacon transmitters 22811 through 22814.

In a further alternate embodiment, where each beacon transmitter alsoincludes receiver locator capability 2180 (not shown), the positions ofthe beacon transmitters may be determined by determining the set ofranges R1 through R4 between available Transceivers and determiningposition by triangulation from the set of ranges R1 through R4.

FIG. 28 is a process flow diagram of a positioning system includingfixed beacon transmitters and mobile locator tags using near fieldsignal strength. The positioning system of FIG. 28 may be used for avariety of applications including but not limited to military oremergency responder applications. A preferred embodiment method for nearfield signal strength positioning begins at a start block 2837 andcontinues (with the following steps in no particular order) with a userdeploying ranging nodes (as noted in block 2890) and a user selectingbuilding type (as noted in block 2886). A user selecting building typeeffects a selection of appropriate ranging parameters 2892 for a rangingalgorithm from stored ranging parameters 2892 for various buildings asshown in block 2891. Alternatively, a user selecting building type (asnoted in block 2886) may select the ranging algorithm optimized for theparticular building type, thus effected the process step denoted inblock 2891. Ranging parameters 2892 may pertain to a particular class ofstructure or may be optimized to particular structures. The rangingparameters 2892 or the ranging algorithm selection (as noted in block2891) may be conveyed to a mobile locator tag by using a data link.Alternatively, the ranging parameters 2892 or the ranging algorithmselection (as noted in block 2891) may be conveyed to a local datacenter (LDC) where a ranging calculation may be performed.

In alternate embodiments, appropriate ranging parameters 2892 for agiven propagation environment may be determined for a particularincident scene by a plurality of beacon transmitters sending signalsthrough the given propagation environment to locator receivers at knownpositions, for instance, co-located with other beacon transmitters.

The preferred embodiment method of FIG. 28 for near field signalstrength positioning continues with a process block 2893 in which amobile locator tag tunes to the i^(th) ranging frequency beginning withi=1. The method continues with the following steps in no particularorder with the mobile locator tag measuring signal strength from abeacon transmitter operating at the i^(th) ranging frequency (as shownin block 2844) and optionally with the mobile locator tag measuringother signal parameters such as signal strength ratio or phaseproperties of a signal from the beacon transmitter operating at thei^(th) ranging frequency (as shown in block 2845). The mobile locatortag employs signal amplitude or RSSI to calculate range using theranging algorithm selected in block 2891 (as shown in block 2894). Themobile locator tag further employs other signal characteristics such assignal strength ratio or phase properties of a signal to determinebearing or other position relevant information (as shown in block 2895).

The method of FIG. 28 continues with a decision block 2896 whether to goto the (i+1)^(th) ranging frequency. If yes, the process continues witha mobile locator tag tuning to the (i+1)^(th) ranging frequency as shownin block 2893. If no, the process continues with a mobile tag conveyingrange and other useful information, including but not limited tobearing, to a local data center (LDC) as shown in block 2897. A localdata center may employ range and other useful information, including butnot limited to bearing, to find location as denoted in block 2898. Inalternate embodiments, a mobile locator tag may employ range and otheruseful information, including but not limited to bearing, to findlocation and convey location information to a local data center (LDC) orelsewhere by using a data link. In still other alternate embodiments, amobile locator tag may convey signal amplitude or RSSI to a local datacenter (LDC) or elsewhere for a calculation of range using a rangingalgorithm. A mobile locator tag may further convey other signalcharacteristics such as signal strength ratio or phase properties of asignal to a local data center (LDC) or elsewhere for a determination ofbearing or other position relevant information.

A preferred embodiment method for near field signal strength positioningcontinues with a decision block 2899 assessing whether to continuetracking based on user inputs or other information. If yes, the processcontinues as shown in block 2993 by a mobile locator tag tuning to thei^(th) ranging frequency beginning with i=1 and repeating. If no, theprocess terminates in an end block 2847.

Orthogonal Antenna Systems

This section presents an evaluation of the geometric orientation forwhich two small loops will have minimum coupling. We assume that theloops lie in each other's near field, so only inductive coupling isrelevant. To solve the problem, the inventors invoke the principal ofreciprocity between two electromagnetic systems, system “a” and system“b.” By the principal of reciprocity:

$\begin{matrix}{{{\int{\int_{V}{\int{\left\lbrack {{E_{b} \cdot J_{a}} - {H_{a} \cdot M_{b}}} \right\rbrack\ {\mathbb{d}V}}}}} = {\int{\int_{V}{\int{\left\lbrack {{E_{a} \cdot J_{b}} - {H_{b} \cdot M_{a}}} \right\rbrack\ {\mathbb{d}V}}}}}}\ } & (1)\end{matrix}$In other words, the interaction between the fields of antenna b (E_(b),H_(b)) and the sources of antenna a (J_(a), M_(a)) must be identical tothe interaction between the fields of antenna a (E_(a), H_(a)) and thesources of antenna b (J_(b), M_(b)).

FIG. 29 shows the geometry around two small orthogonal loops. A firstsmall loop antenna (loop a) 2904 is characterized by a magnetic momentM_(a) in the +z-direction and a second small loop antenna (loop b) 2908is characterized by a magnetic moment M_(b) in the −y-direction.Ignoring far field terms, the magnetic field of a first small loopantenna 2904 is given by:H _(a) =H _(a)(2 cos θ{circumflex over (r)}+sin θ{circumflex over(θ)})  (2)The magnetic moment of a second small loop antenna 2908 is given by:M _(b) =−M _(y) ŷ=−M _(y)(sin θ sin φ{circumflex over (r)}+cos θ sinφ{circumflex over (θ)}+cos φ{circumflex over (φ)})  (3)Setting H_(a)·M_(b)=0 yields:

$\begin{matrix}\begin{matrix}{0 = {H_{a} \cdot M_{b}}} \\{= {{- \left( {{2\cos\;\theta\;\hat{r}} + {\sin\;\theta\;\hat{\theta}}} \right)} \cdot \left( {{\sin\;{\theta sin}\;\phi\;\hat{r}} + {\cos\;{\theta sin}\;\phi\;\hat{\theta}} + {\cos\;\phi\;\hat{\varphi}}} \right)}} \\{= {{- 3}\cos\;{\theta sin}\;\theta\;\sin\;\phi}}\end{matrix} & (4)\end{matrix}$The result of (4) is zero if sin θ=0, cos θ=0, or sin φ=0. Thus θ=0°,90°, or 180° or φ=0°, or 180° yields no coupling between the loops. Aminimal coupling orientation between a first small loop antenna 2904(loop a) and a second small orthogonal loop antenna 2908 (loop b) is onewhich satisfies (4). Geometrically, a minimum coupling orientation (orarrangement) will occur when one loop lies either in the plane or alongthe axis of the other.

FIG. 30 shows the geometry around two small orthogonal loops in a firstminimal coupling arrangement. In a first minimal coupling arrangement ofsmall orthogonal loops, a second loop 3008 lies in the plane of a firstloop 3004. Angle θ_(ab) from an axis of a first loop 3004 to thedirection of a second loop 3008 is a right angle. A first minimalcoupling arrangement of small orthogonal loops (as shown in FIG. 30)corresponds to a second small loop antenna 3008 (loop b) located atθ=90° and φ=90° relative to a first small loop antenna 3004 (loop a).

FIG. 31 shows the geometry around two small orthogonal loops in a secondminimal coupling arrangement. In a second minimal coupling arrangementof small orthogonal loops, a second loop 3108 lies in the plane of afirst loop 3104 and a first loop 3104 lies in the plane of a second loop3108. Angle θ_(ab) from an axis of a first loop 3104 to the direction ofa second loop 3108 is a right angle. Similarly angle θ_(ba) from an axisof a second loop 3108 to the direction of a first loop 3104 is a rightangle. A second minimal coupling arrangement of small orthogonal loops(as shown in FIG. 31) corresponds to a second small loop antenna 3108(loop b) located at θ=90° and φ=0° relative to a first small loopantenna 3104 (loop a).

The inventors have found that although in theory the minimal couplingarrangements of FIG. 30 and FIG. 31 should be equivalent, in practicethe arrangement of FIG. 31 yields lower mutual coupling under manycircumstances. Having both a first loop 3104 and a second loop 3108 eachin the plane of the other yields lower mutual coupling. Other factorsincluding ergonomic and mechanical factors may further influence choiceof an arrangement.

FIG. 32 shows two small orthogonal loop antennas in a first minimalcoupling arrangement for a compact tracking device 3200. Compacttracking device 3200 comprises RF module 412, enclosure 3299, and aspace efficient magnetic antenna system 3298 further comprising a firstmagnetic antenna 3204 and a second magnetic antenna 3208. A firstmagnetic antenna 3204 has a null generally aligned along first null axis405. A second magnetic antenna 3408 has a null generally aligned alongsecond null axis 409. A first null axis 405 is substantially orthogonalto a second null axis 409.

A first magnetic antenna system 3204 further comprises a first magneticantenna component 3213 and a second magnetic antenna component 3214(collectively, a “first set of magnetic antenna components”). A firstset of magnetic antenna components is generally aligned along axesco-parallel to a first null axis 405. A first magnetic antenna system3204 is depicted as having two components for purpose of illustrationand not limitation. In alternate embodiments, a first magnetic antennasystem 3204 may further comprise more than two components or a singlecomponent.

A second magnetic antenna system 3208 further comprises a third magneticantenna component 3217 and a fourth magnetic antenna component 3218(collectively, “second set of magnetic antenna components”). A secondset of magnetic antenna components are all generally aligned along axesco-parallel to second null axis 409. A second magnetic antenna system3208 is depicted as having two components for purpose of illustrationand not limitation. In alternate embodiments, a second magnetic antennasystem 3208 may further comprise more than two components or a singlecomponent.

FIG. 33 shows two small orthogonal loop antennas in a second minimalcoupling arrangement for a compact tracking device 3300. Compacttracking device 3300 includes RF module 412, enclosure 3399, and a spaceefficient magnetic antenna system 3398 further comprising first magneticantenna 3304 and second magnetic antenna 3308. First magnetic antenna3304 has a null generally aligned along first null axis 405. Secondmagnetic antenna 3308 has a null generally aligned along second nullaxis 409. First null axis 405 is substantially orthogonal to second nullaxis 409.

A first magnetic antenna system 3304 further comprises a first magneticantenna component 3313 and a second magnetic antenna component 3314(collectively, “first set of magnetic antenna components”). A first setof magnetic antenna components are all generally aligned along axesco-parallel to first null axis 405. A first magnetic antenna system 3304is depicted as having two components for purpose of illustration and notlimitation. In alternate embodiments, a first magnetic antenna system3304 may further comprise more than two components or a singlecomponent.

A second magnetic antenna system 3308 further comprises a third magneticantenna component 3317 and a fourth magnetic antenna component 3318(collectively, a “second set of magnetic antenna components”). A secondset of magnetic antenna components are all generally aligned along axesco-parallel to a second null axis 409. A second magnetic antenna system3308 is depicted as having two components for purpose of illustrationand not limitation. In alternate embodiments, a second magnetic antennasystem 3208 may further comprise more than two components or a singlecomponent.

FIG. 34 presents a potential circuit diagram for a magnetic loopstickantenna 3304. A magnetic loopstick antenna 3304 comprises a firstmagnetic antenna component 3313 and a second magnetic antenna component3314 (collectively, “a set of magnetic antenna components”). In apreferred embodiment, a magnetic loopstick antenna 3304 furthercomprises tuning means 3332, a secondary coupling coil 3333 and couplingcoil terminals 3334.

A first set of magnetic antenna components are aligned and connected soas to have a generally constructive addition of patterns substantiallyalong pattern axis 407 and nulls generally co-parallel with null axis405. For best results, the sense of currents in a first magnetic antennacomponent 3313 and a second magnetic antenna component 3314 should bethe same so that the patterns of a set of magnetic components add upconstructively. Similarly for best results, secondary coupling coil 3333should couple to each of a set of magnetic components with the samesense so as to yield maximal transmission of power (or conversely,maximal sensitivity to received signals) from coupling coil terminals3334.

A set of magnetic antenna components may be loopstick antenna or otherinductive components. In preferred embodiments, a set of magneticcomponents do not share a common ferrite core.

FIG. 35 shows a space efficient magnetic antenna system 3598 with asmall orthogonal loop antenna 3508 characterized by a null axis 409orthogonal to a principal axis 3550. In an alternate embodiment, a spaceefficient magnetic antenna system 3598 comprises a first magneticantenna 3504 and a second magnetic antenna 3508. A first magneticantenna 3504 further comprises a first bar 3502, a first primary coil3501, and a first secondary coil 3503. A second magnetic antenna 3508further comprises a second bar 3505, a second primary coil 3506, and asecond secondary coil 3507. A first magnetic antenna 3504 has first nullaxis 405. A second magnetic antenna 3508 has second null axis 409. Asecond null axis 409 is substantially orthogonal to a first null axis405. A second bar 3505 has a principal axis 3550. A principal axis 3550is preferentially an axis of symmetry of a second bar 3505. In addition,a principal axis 3550 is substantially aligned with the dimension ofgreatest extent of a second bar 3505. A second primary coil 3506, and asecond secondary coil 3507 cooperate with a second bar 3505 to create anull axis 409 substantially orthogonal to a principal axis 3550. A firstbar 3502 and a second bar 3505 are preferentially ferrite bars, but inalternate embodiments may be any other material suitable for use in amagnetic antenna. In the context of the present invention, terms like“rod,” “bar,” or “core” may be used interchangeably to refer to amaterial incorporated in a magnetic antenna for either mechanicalsupport or for the benefit of high permeability.

In many prior art loopstick antennas (like that of FIG. 1) loopstickaxis 205 is both a principal axis as well as a null axis. In thealternate embodiment of FIG. 35, a second magnetic antenna 3508 ischaracterized by a null axis 409 that is not substantially co-parallelto a principal axis 3505. In fact, in the alternate embodiment of FIG.35 a null axis 409 is substantially orthogonal to a principal axis 3505.A space efficient magnetic antenna system 3598 further cooperates withan RF module 412 and an enclosure 3599 to create a compact trackingdevice 3500.

FIG. 36 shows a space efficient magnetic antenna system 3698 with threemutually orthogonal magnetic antennas on a common core 3602. Spaceefficient magnetic antenna system 3698 comprises three mutuallyorthogonal antennas. A first primary coil 3601, a first secondary coil3603, and a common core 3602 cooperate as a first magnetic antenna witha first null axis 405. A second primary coil 3606, a second secondarycoil 3607, and a common core 3602 cooperate as a second magnetic antennawith a second null axis 409. A second null axis 409 is substantiallyorthogonal to a first null axis 405. A third primary coil 3609, a thirdsecondary coil 3610, and a common core 3602 cooperate as a thirdmagnetic antenna with a third null axis 3629. A third null axis 3629 issubstantially mutually orthogonal to a first null axis 405 and a secondnull axis 409. Compact tracking device 3600 includes RF module 412,enclosure 3699, and a space efficient magnetic antenna system 3698. Inalternate embodiments, a space efficient magnetic antenna system 3698may comprise either one or two magnetic antennas.

A first null axis 405 is also a principal axis 405 of a common core3602. A principal axis 405 of a common core 3602 is generally alignedwith the dimension of greatest extent of a common core 3602. Thus asecond magnetic antenna is characterized by a second null axis 409 thatis substantially orthogonal to a principal axis 405 of an associatedcommon ferrite core 3602. A common core 3602 is preferentially a ferritecore, but in alternate embodiments may be any other material suitablefor use in a magnetic antenna.

A second null axis 409 is also a secondary axis 409 of a common core3602. A common core 3602 is shown with much less extent along asecondary axis 409 than along a principal axis 405. A substantialdifference in extent along a secondary axis 409 relative to a principalaxis 405 is beneficial for enabling a compact tracking device with a lowprofile form factor, such as a “credit-card” form factor. In alternateembodiments, there may be no substantial difference in extent along asecondary axis 409 relative to a principal axis 405.

Although the present invention is illustrated in terms of ferritematerials, one skilled in the RF arts will realize that other magneticmaterials (like iron), non-magnetic materials (like plastic or printedcircuit board materials), an air core, or even meta-materials may beacceptable substitutes or alternatives for ferrite in a magneticantenna. Thus, use of terms like “ferrite” in the present inventionshould be understood as being illustrative, not limiting.

A space efficient magnetic antenna system is of particular value inconjunction with an RF module and when used as a component in a systemfor wireless tracking. Magnetic antennas are well suited forapplications requiring an antenna to be mounted against a human body, anasset, or other objects being tracked. Further, a space efficientmagnetic antenna system enables a compact tracking device. A compacttracking device is highly prized in a wireless tracking application.

Specific applications have been presented solely for purposes ofillustration to aid the reader in understanding a few of the great manycontexts in which the present invention will prove useful. It shouldalso be understood that, while the detailed drawings and specificexamples given describe preferred embodiments of the invention, they arefor purposes of illustration only, that the system and method of thepresent invention are not limited to the precise details and conditionsdisclosed and that various changes may be made therein without departingfrom the spirit of the invention.

1. A space efficient magnetic antenna system, comprising: a firstmagnetic antenna, said first magnetic antenna having a first null axisaligned within a predetermined plane, said first magnetic antennafurther comprising a plurality of interconnected magnetic antennaelements, each said magnetic antenna element having a null axissubstantially parallel to said first null axis; and a second magneticantenna, said second magnetic antenna having a second null axis alignedsubstantially orthogonal to said first null axis and said second nullaxis further aligned within said predetermined plane.
 2. The system ofclaim 1, wherein said second magnetic antenna lies in a minimal couplingorientation with respect to said first magnetic antenna.
 3. The spaceefficient magnetic antenna system of claim 1, wherein said firstmagnetic antenna comprises a coil wound around a loopstick axis, saidcoil having turns lying parallel to a plane, said plane at a substantialdiagonal angle from said loopstick axis.
 4. The space efficient magneticantenna system of claim 1, further including an RF module having atleast one characteristic physical dimension, wherein said first magneticantenna has a null axis at a substantial diagonal angle from said atleast one characteristic physical dimension.
 5. The space efficientmagnetic antenna system of claim 4, wherein the at least onecharacteristic physical dimension is one of the group consisting ofoverall length, overall width, and overall height.
 6. The spaceefficient magnetic antenna system of claim 1, wherein the first magneticantenna and second magnetic antenna are embedded in clothing and thenull axis of said first magnetic antenna is substantially perpendicularto the null axis of said second magnetic antenna, said null axes lyingsubstantially in an azimuthal plane.
 7. The space efficient magneticantenna system of claim 1, further including an RF module wherein saidRF module alternately utilizes said first magnetic antenna and saidsecond magnetic antenna.
 8. The space efficient magnetic antenna systemof claim 1, further including an RF module wherein said RF module drivessaid second magnetic antenna in phase quadrature relative to said firstmagnetic antenna.
 9. The space efficient magnetic antenna system ofclaim 1, further including a third magnetic antenna with a third nullaxis mutually orthogonal to said first null axis and said second nullaxis.
 10. A space efficient magnetic antenna system, comprising: a firstmagnetic antenna, said first magnetic antenna having a first null axisaligned within a predetermined plane, and a second magnetic antennahaving a second null axis aligned substantially orthogonal to said firstnull axis and said second null axis further aligned within saidpredetermined plane; wherein said second magnetic antenna lies in aminimal coupling orientation with respect to said first magneticantenna.
 11. The space efficient magnetic antenna system of claim 10,wherein said first magnetic antenna further comprises a plurality ofinterconnected magnetic antenna elements, each said magnetic antennaelement having a null axis substantially parallel to said first nullaxis.
 12. The space efficient magnetic antenna system of claim 10,further including an RF module wherein said RF module alternatelyutilizes said first magnetic antenna and said second magnetic antenna.13. The space efficient magnetic antenna system of claim 10, furtherincluding an RF module wherein said RF module drives said secondmagnetic antenna in phase quadrature relative to said first magneticantenna.
 14. The space efficient magnetic antenna system of claim 10,further including an RF module having at least one characteristicphysical dimension, wherein said first magnetic antenna has a null axisat a substantial diagonal angle from said at least one characteristicphysical dimension.
 15. The space efficient magnetic antenna system ofclaim 10, further including a third magnetic antenna with a third nullaxis mutually orthogonal to said first null axis and said second nullaxis.
 16. The space efficient magnetic antenna system of claim 10,wherein said first magnetic antenna further comprises a bar, said bar ischaracterized by a principal axis, said principal axis is characterizedby an orientation relative to said first null axis, and said orientationof said principal axis is not substantially co-parallel to said firstnull axis.
 17. A space efficient magnetic antenna system, comprising: afirst magnetic antenna, said first magnetic antenna having a first nullaxis aligned within a predetermined plane, and a second magnetic antennahaving a second null axis aligned substantially orthogonal to said firstnull axis and said second null axis further aligned within saidpredetermined plane, said first magnetic antenna and said secondmagnetic antenna further including a common core.
 18. The spaceefficient magnetic antenna system of claim 17, wherein said common coreis characterized by a principal axis, wherein said common core ischaracterized by a secondary axis, and wherein there is a substantialdifference in extent in said common core along said secondary axisrelative to said principal axis.
 19. The space efficient magneticantenna system of claim 18, further including an RF module wherein saidRF module drives said second magnetic antenna in phase quadraturerelative to said first magnetic antenna.